This invention relates generally to methods and apparatus for removing photoresist from the surfaces of substrates, and specifically to methods and apparatus for removing photoresist from silicon semiconductor wafers using ozonated deionized water.
The need for quick and efficient removal of photoresist is critical in the area of semiconductor manufacturing. In order to produce a useful semiconductor wafer, first a silicon crystal is grown, sliced into thin wafers, and exposed to a photoresist which forms a layer on the wafers. Multiple layers of photoresist can be formed on the surface of the wafers and then etched off to form patterns on the wafers.
The use of DIO3, which is a mixture of chilled distilled water (DI) and ozone (O3), to remove photoresist from surfaces of a silicon wafer has been taught by Matthews in U.S. Pat. No. 5,776,296. Matthews discloses a process and an apparatus for removing photoresist from a semiconductor wafer using DIO3 at sub-ambient temperatures of 1 to 15xc2x0 C. wherein the ozone is introduced into the process tank with xe2x80x9ca composite element having a permeable member and a nonpermeable member, the permeable member having a top portion and a bottom portion, a means defining an open space in a center portion of the permeable member, and a means defining a trench positioned on the top portion of the permeable member between an outer periphery of the permeable member and the means defining an open space.xe2x80x9d The Matthews system suffers from certain disadvantages in photoresist removal.
Specifically, requiring that the DIO3 be at a sub-ambient temperature necessitates the use of a chiller, which can be expensive and occupy valuable space in manufacturing clean rooms. Additionally, the Matthews system and methods are not optimal with respect to the speed, efficiency, and effectiveness.
Another method of photoresist stripping is taught by Honda et al in U.S. Pat. No. 6,103,680. Honda teaches applying ozonated water to a semiconductor wafer through the use of a spray rinse to strip photoresist from the wafer. However, the strip rates achieved by merely spraying the wafers with ozonated water are less than optimal with respect to the speed, efficiency, and effectiveness. Thus, a need exists to improve this stripping process.
It is an object of the present invention to provide an improved process of removal of photoresist from semiconductor wafers during the manufacture thereof. Another object is to provide a process and system at high rates and efficiency.
These objects, and others which will become apparant from the following disclosure and the accompanying drawings, are achieved by the present invention which in one aspect is a method of removing photoresist from silicon wafers comprising: positioning at least one semiconductor wafer having at least one layer of photoresist in a process tank; providing ozone gas to said process tank; and spraying said semiconductor wafer with a mixture of ozone and deionized water (DIO3) via at least one nozzle.
Preferably, the ozone gas in the process tank will be under pressure as the semiconductor wafers are being sprayed with the DIO3. This pressure can be between 1 to 3 atmospheres. Also preferably, the nozzles should be high pressure nozzles. The DIO3 can then be sprayed at a nozzle pressure between 1 to 10 atmospheres from said nozzles, preferably between 5 to 10 atmospheres.
The process can also include keeping the temperature in the processing tank at or above ambient temperature. In one embodiment, the temperature is kept between 20-50xc2x0 C. The process can further include the step of recirculating the DIO3 back into said process tank via said nozzle. When recirculation is used, additional ozone should be added to the DIO3 during recirculation thereby keeping the concentration of ozone in said mixture about constant. This mixture of deionized water and ozone can then be agitated via at least one nozzle. Also, the mixture of deionized water and ozone can be sprayed as a vapor into said process tank or can be sprayed into said process tank as droplets.
In another aspect, the invention is an apparatus for the removal of photoresist from semiconductor wafers, comprising: a process tank capable of holding at least one semiconductor wafer; at least one nozzle set within said tank, said nozzle adapted to spray a mixture of deionized water and ozone onto said wafer; and a source of ozone connected to said process tank.
Preferably, the apparatus will further comprise a means to pressurize said process tank and a means for recirculating said mixture of deionized water and ozone back to said nozzle. The recirculation means should comprise a filter so that photoresist that is stripped off the wafers is not reapplied by the nozzles. Additionally, the means for recirculating can be connected to the source of ozone so that the concentration of ozone in the mixture being applied to the wafers via the nozzles is approximately constant.
It is further referable that the nozzles be high pressure nozzles capable of spraying said mixture of deionized water and ozone at a pressure between 1 and 10 atmospheres. The apparatus should further comprise a means for temperature control adapted to maintain temperature in said process tank between above 20-50xc2x0 C.
The apparatus can further comprise an ozonator in fluid connection with said nozzle. The source of ozone can be an ozone generator and the nozzle is preferably at or near the top of the process tank.
Preferably a pressure plenum set in excess of one atmosphere, a temperature control system, an ozonator, a filter connected to the tank, and a recirculating pump are included. It is further preferred that the temperature controller is set to maintain the liquid temperature at 20-21xc2x0 C. or higher.
The DIO3 water mixture can be exposed to the photoresist in the form of a fog and/or tiny droplets of water. The concentration level of the gaseous and dissolved ozone can be monitored using inline ozone analyzers.
Agitation of the DIO3 water on the photoresist layers raises the rate of photoresist removal, i.e., the xe2x80x9cstrip ratexe2x80x9d for photoresist treated with DIO3 water is linked to the velocity rate of the DIO3 water. Notably, an increase in the fluid velocity reduces the boundary layer thickness, thereby resulting in a higher rate of O3 oxidizing the photoresist (also known as xe2x80x9cthe etching ratexe2x80x9d). Fluid velocity of the mixture coming from the nozzles increases with nozzle pressure. In addition, the use of sonic energy also reduces the boundary layer thickness, again resulting in a higher rate of O3 oxidizing the photoresist or etch rate. Thus, the higher the kinetic energy and O3 concentration, the shorter the strip time.